1. Field of the Invention
This invention relates to a magnetic tape cassette, and more particularly to a magnetic tape cassette comprising a digital audio tape and a cassette casing for accommodating the digital audio tape having a slider member which is moved to an open position to give access to the tape in response to loading the cassette in a recording and/or reproduction system.
2. Description of the Prior Art
There has been known a DAT cassette comprising a digital audio tape and a cassette casing for accommodating the digital audio tape. The cassette casing for the DAT cassette has a slider member which is slidable between an open position and a closed position. The slider member is normally spring-urged to the closed position and held in the closed position by a slider lock means. When the cassette is loaded in a cassette deck, a lock release member provided in the cassette deck releases the slider member from the slider lock means and pushes the slider member relative to casing body to the open position, where the slider lock member again engages with the slider member to lock it in the open position.
More particularly, the slider member is mounted on the lower side of the casing body to be slidable relative to the casing body in the direction of insertion of the DAT cassette into the cassette deck. The slider member has a pair of guide grooves extending from the leading end of the slider member to an intermediate portion thereof, and the cassette deck is provided with a pair of lock release projections. When the DAT cassette is inserted into the cassette deck, the lock release projections are respectively received in the guide grooves and move along the guide grooves relative to the slider member. First and second engaging holes are provided in the bottom of each of the guide grooves spaced from each other in the longitudinal direction of the guide groove. A pair of lock members each having a locking projection which is adapted to be engaged with the first and second engaging holes are provided on the casing body and are resiliently urged toward the upper surface of the slider member. When the slider member is in the closed position, the locking projections of the lock members are engaged with the first engaging holes of the slider member, whereby the slider member is held in the closed position.
When the lock release projections abut against the locking projections of the lock members as the DAT cassette is inserted into the cassette deck, the lock release projections push upward the locking projections to disengage them from the first engaging holes, and thereafter the lock release projections abut against the end faces of the respective guide grooves. Since the locking projections have been disengaged from the first engaging holes of the slider member, the slider member is slid relative to the casing body toward the open position as the DAT cassette is further inserted into the cassette deck while the locking projections slide along the upper surface of the slider member.
When the DAT cassette is completely inserted into the cassette deck, the slider member reaches the open position and the locking projections are brought into engagement with the second engaging holes to hold the slider member in the open position.
However, in the conventional DAT cassettes, much trouble has occurred in opening and closing of the slider member.
For example, in the conventional DAT cassettes, the lower surface of the slider member and the upper surface of the cassette deck which is opposed to the lower surface of the slider member and on which the lock release projections are provided are both designed to be flat. However, when the latter surface is concave in the direction of width of the DAT cassette, i.e., when both side portions of the latter surface are higher than that of the middle portion, for some reason of production, both side portions of the slider member ride on the side portions of the surface of the cassette deck and the distance between the locking projections and the lock release projections is enlarged, whereby the locking projections cannot be lifted by an amount sufficient to disengage the locking projections from the first or second engaging holes.
Further, in the conventional DAT cassette, the locking projections can be caught by the edges of the engaging holes, which prevents insertion of the DAT cassette into the cassette deck and/or release of the slider member from the lock members.